This application claims the priority of German Patent Application No. DE 101 40 599.5 filed Aug. 18, 2001, which is incorporated herein by reference.
The invention relates to a cartridge with a combustible cartridge case containing a propellant charge and an electrothermal ignition device or igniter.
In order to ignite the propellant powder of known cartridges with an electrothermal ignition device, an extremely high current is allowed to flow through a wire conductor in the bottom region of the respective cartridge, which is high enough to cause an explosive vaporization, of the wire thus generating an energy-rich electric arc. The electric arc then ignites the respective propellant powder.
It has turned out to be a disadvantage of the known cartridge that only a relatively small percentage of the propellant powder is initially ignited when generating the electric arc on the bottom side. Frequently, this does not result in a reproducible burning behavior of the propellant charge, particularly with hard to ignite propellant powders, i.e., low vunerability ammunition (LOVA).
Also known is a cartridge with an ignition device that consists of several ignition channels, arranged axially symmetrical in a longitudinal direction of the cartridge. Each ignition channel comprises a propellant tube provided on its inside surface with an electrically conducting layer. If the respective conducting layer is connected to a power-supply system for igniting the charge, it is designed to vaporize abruptly and an electric arc plasma channel is created inside the respective propellant tube, through which current continues to flow. In the process, high-output energy is released to the environment in the form of radiation, thus resulting in a rapid ignition of the propellant tubes and the fragmentation of these tubes. The burning fragments of the propellant tubes, as well as the released electric arc radiation subsequently cause a quick and uniform ignition of the main propellant change.
However, practical experiments have shown that with this known cartridge, it is frequently not possible to produce several parallel electric arcs, despite electrically parallel-connected and axially symmetrical ignition channels. Rather, only one electric arc is initially ignited following the wire explosion, which then prevents the ignition of the additional, parallel electric arcs because of the drop in its current-voltage characteristic. As a result, asymmetrical, radial pressure waves develop, which can damage or destroy, for example, the projectile fin assembly and the weapon. To be sure, the ignition channels and thus also the electric arcs could be electrically separated and each ignition channel could be assigned a separate energy-supply system. However, this would result in an extremely expensive weapon system requiring a lot of space.
The object of the present invention is to provide a cartridge of the aforementioned type, for which a uniform and symmetrical ignition in the chamber of the respective weapon is possible, without requiring additional power-supply systems.
This object generally is achieved according to the present invention which is essentially based on the idea of decoupling the electric arcs by replacing the uniform, electrically conducting layer in each propellant tube with a conductive structure, consisting of successively point connected rhombi, rectangles, circles or ovals, which are arranged planar on the inside or outside of each powder tube and electrically assume the function of decoupling resistances. When current flows through a structure of this type, the connecting bridges arranged in the current-flow direction between the individual rhombi or other structures will first explode because of the ohmic overheating. Electric arcs then form at these locations, which are separated owing to the conductive structures with the resistive resistances. During the continued current flow, the decoupling elements erode even more, so that the electric arcs become longer and longer.
The exact geometry of the rhombi, such as width, length, thickness and material selection is based on the desired resistance values for the decoupling resistances.
The electrically conducting layer can be deposited directly onto the inside or outside surface of the respective propellant tube. However, it is also possible to provide a foil layer of a plastic over the inside or outside surface of the powder tube, onto which the electrically conducting layer can then be deposited. The foil can be a commercially available plastic foil, preferably consisting of polyester or polyethylene. The vapor-deposited structure preferably consists of aluminum or copper.
To ensure a secure and uniform ignition in each of the ignition channels, it has proven useful if an electrically conducting layer is vapor-deposited onto the inside or outside surface of the respective propellant tube. This layer comprises several, preferably three, parallel series connections of decoupling resistances that are joined together.
The length of the ignition channels can range from 50 to 400 mm and preferably ranges from 200 to 300 mm.
With another embodiment of the invention, for which the electrically conducting layer is arranged on the inside surface of the powder tube, an additional propellant tube or rod directly adjoins the conducting layer on the inside. As a result, the loading density of the cartridge can be increased even further.
Additional details and advantages of the invention follow from the exemplary embodiment below, which is explained with the aid of Figures.